This invention relates to a process for producing alloys of active metals formed directly from their salts by molten salt electrolysis. One embodiment of this invention relates to a process for preparing a calcium and magnesium alloy.
The field of new metals and alloys has been growing rapidly as materials with new and better properties are needed. The use of a molten salt electrolysis process for the codeposition of metal alloys and the use of liquid metal cathodes in such processes are known. For example, calcium-lead alloys of 0.6% calcium are produced using liquid metal lead cathodes. The calcium-lead alloy is used in the production of lead plates for sulfuric acid batteries.
Magnesium as a liquid cathode has been used in a molten salt electrolysis process for preparing rare earth metal alloys as described in U.S. Pat. No. 3,729,397. The process of U.S. Pat. No. 3,729,397 includes adding a rare earth metal oxide as feed material to a fused salt bath comprising the fluorides of the rare earth metal and an alkali metal fluoride with the optional inclusion of an alkaline earth metal fluoride, and electrolyzing the electrolyte mixture using carbon anodes and as a cathode, molten magnesium which floats on the electrolyte mixture. The above process has several disadvantages including: evolution of fluorine gas at the anodes, high temperatures are needed to make fluoride salts molten.
U.S. Pat. No. 4,738,759 discloses a method for electrodepositing calcium or a calcium alloy to a liquid cathode of aluminum, tin, copper, lead or bismuth by electrolysis of a calcium derivative in a bath of molten salts based on calcium halides. The disadvantages of the above process include the use of relatively expensive calcium sources such as calcium carbide, calcium silicide, or calcium silicon and the necessity to take product from bottom of cell due to high density of liquid cathode metal.
While molten cathodes have been used to form alloys previously, molten magnesium cathodes have not been used to form alloys of reactive metals such as calcium. Active metals such as calcium, lithium, sodium and potassium are quite reactive and difficult to handle and prepare. Calcium-magnesium products, such as PELAMAG.RTM., have been used in the steel industries. However, these products have been formed by physical mixing using pure calcium and magnesium compounds. Another method which has been used in the prior art to form a calcium-magnesium product includes impregnating a magnesium with calcium oxide.
Calcium-magnesium products produced by the prior art methods have low levels of calcium in the alloy. It is desired, therefore, to provide a process for producing a calcium-magnesium product with a much higher level of active calcium.
It is further desired to provide a process for producing alloys of active metals formed directly from their salts by molten salt electrolysis, more particularly, a process of electrodepositing the active metals directly into a molten magnesium cathode from a molten salt bath to form an alloy of magnesium and the respective active metal.
It is further desired to provide a process for producing a magnesium-active metal alloy which is much less reactive towards air than the active metal itself, and which is less reactive than magnesium.
It is desired to provide a cell where liquid magnesium in contact with a current source is the cathode in a molten salt system such that a reactive metal, for example lithium or calcium, can be electrowon from a molten salt bath forming an alloy at the molten magnesium cathode resulting in a molten alloy.
It is further desired to produce a calcium-magnesium product for use in the steel industry as a desulfurizer and dephosphorizer without having to handle calcium metal, because as aforementioned, calcium metal in its isolated form is a difficult to handle metal due to its reactivity.
An object of this invention is to produce an easy to handle calcium compound which can be used, for example, as a reducing agent in the metallothermic reduction of neodymium oxide or chloride and in many other applications where calcium is conventionally used.